The present invention relates to a double-feed prevention device in paper feeding apparatus, and more particularly, to such a device especially adapted to avoid the double-feed of paper sheets which tends to occur due to the wear of a surface of a paper feeding roller.
In paper feeding apparatus used for various machines such as printing, copying, paper folding and the like, it is highly desirable to feed single sheets of paper from a stack of paper sheets placed on a paper feeding plate. There are many known prior art devices for single sheet feeding of paper.
A particularly reliable single sheet feed device is disclosed in Japanese Patent No. 850580. In accordance with this patent, a paper feeding roller is opposed by a paper separating plate having a friction member mounted thereon. The paper separating plate is resiliently biased by a lever toward the paper feeding roller. The paper sheets fed between the feeding roller and the friction member being separated into single sheets of paper from the other sheets in the same manner as two sheets of paper are separated by hand by slipping one off the other with relative movement between the thumb and index finger.
The above prior art apparatus requires careful selection of the force biasing the paper separating plate against the paper feeding roller since paper buckling and jamming results if the biasing force is too high, or double sheet feed results if the force is too low. In order to improve the feed reliability of this device, an adjustable fixed mechanical stop is used to regulate the position of the paper separating plate. The stop is adjusted to prevent a gap between the friction member and the paper feeding roller from widening beyond a dimension or thickness corresponding with that of a single sheet of paper.
The use of such stops in prior feed devices has not been entirely satisfactory since wear of opposed members requires frequent adjustment of the stops. Further, the required adjustments are too delicate and troublesome to be done efficiently using conventional manual procedures.
Also, when any buckling or jamming of a paper sheet occurs, such jammed paper sheet must be removed from the device by releasing the stopper, and thereafter the stopper must be re-adjusted by delicate manual operation.